1. Field
The present inventive concept relates to a semiconductor device and a method for fabricating the same.
2. Description of the Prior Art
As the feature size of a MOS transistor is decreased, the lengths of a gate and a channel that is formed below the gate become short. Accordingly, various research has been performed to increase capacitance between the gate and the channel and to improve operation characteristics of the MOS transistor.
A MOS (Metal-Oxide-Semiconductor) transistor using a polysilicon gate electrode has been widely used. Since a polysilicon material can endure high temperature in comparison to most metals, polysilicon may be annealed at high temperatures together with source and drain regions. Further, since polysilicon can prevent ion implantation of atoms that are doped in a channel region, it becomes possible to form the polysilicon in a self-aligned source/drain structure after gate patterning is completed.
On the other hand, since the polysilicon material has high resistance in comparison to most metal material, a polysilicon gate electrode operates at lower speed than a gate that is made of a metal material. In order to compensate for the high resistance of the polysilicon material, a method for replacing the polysilicon gate electrode by a metal gate electrode may be used. This method may be performed using an RMG (Replacement Metal Gate) process, in which a high-temperature process is performed while the polysilicon exists on a semiconductor substrate, and after the process, a replacement metal gate is formed through removal and replacement of the polysilicon by a metal.